1. Field of the Invention
The present invention is directed to a transition joint or coupling for a fluid delivery system wherein a transition is made between a plastic and a metal pipe or piping system.
2. Prior Art
The present transition joint coupling is a xe2x80x9cstab-typexe2x80x9d or xe2x80x9cgripper-typexe2x80x9d coupler wherein the plastic pipe may be inserted in an axial direction manually into the pre-assembled coupler which is then tightened with a wrench. The gripper-type coupler serves to form a sealed, leak-proof communication which may be installed in the field with simple tools. Gripper-type couplers are common in the prior art and consist generally of an adapter nut having a passageway therethrough, a first end with external threads and an opposed, second end having internal threads. The adapter nut typically includes a recess having a shoulder which will receive a rigid metal stiffener tube. A hollow gripper having a frusto-conical external surface is positioned within a recess in an adapter coupling. The gripper has an internal circumferential surface configured to grippingly engage the plastic pipe and an elastomeric compression ring which seals with the outside surface of the plastic pipe. As the adapter coupling is tightened the gripper digs into the plastic pipe and the compression ring seals the outside surface of the plastic pipe.
Experience by users of the gripper-type couplings that exist in the prior art has shown that nicks or cuts in the outer surface of the plastic pipe may adversely affect the seal between the coupling and the outer surface of the plastic pipe. This is an obvious disadvantage to the product found in the prior art. The present invention provides a gripper coupling having a mechanism to provide a leak-proof seal with the interior surface of the plastic pipe. Examples of gripper-type couplings as exist in the prior art may be seen in the 1996 Continental Industries Catalog, Page S4.1.1. Examples of pipe couplings that seal to the interior surface of the plastic pipe can be seen in assignee""s patents such as U.S. Pat. Nos. 5,791,698 and 5,692,785 which cover stab-type couplers.
The present invention may be used in numerous applications involving various fluids such as but not limited to natural gas or water. In many applications today, natural gas is transported within a plastic pipe, such as polyethylene, while passing underground. The plastic pipe is lighter and easier to handle than metal and is not subject to corrosion. Various governmental and other regulations require that if a pipe goes above ground or goes within a building, the piping must be metal. In some cases, a transition will be made from plastic to metal piping. In other cases, the plastic pipe will be sheathed with a metal pipe.
Finally, in some applications, old metal piping systems must be repaired or replaced. As an alternative thereto, plastic piping may be inserted within the existing metal piping or xe2x80x9cslip-linedxe2x80x9d. This avoids the requirement of digging a new trench.
It is, therefor, a principal object and purpose of the present invention to provide a transition joint or coupling to connect a metal piping system with a plastic piping system which forms a seal not with the exterior of the plastic pipe but instead with the inside diameter or surface of the plastic pipe.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in this application to the details of construction and to the arrangement so that the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
The present invention provides a transition joint or coupling between a plastic piping system and a metal piping system. In one embodiment for use as a service head adapter, the transition coupling includes an adapter nut having a passageway therethrough, a first end with external threads and an opposed, second end having internal threads. The adapter nut includes a recess having a shoulder which will receive a rigid stiffener tube which is positioned coaxially within the adapter nut. The rigid stiffener tube could be made out of metal, hard plastic or any other material having like properties. A portion of the rigid stiffener tube includes an external knurled cylindrical surface. An O-ring or toroidal elastomeric seal is inserted over a circumferential groove in the rigid stiffener tube. Additionally, an O-ring or toroidal elastomeric seal or seals are inserted over a groove or grooves in the rigid stiffener tube. The seals are not strictly limited to O-rings or toroidal elastomeric seals in a groove but could be molded in place or any other configuration or material designed to provide a seal with inside surface of the pipe.
A hollow gripper having a frusto-conical external surface is positioned within a recess in an adapter coupling. The gripper has an internal circumferential surface configured to grippingly engage the plastic pipe.
The adapter coupling has an opening therethrough and is connected to the adapter nut by external threads on the adapter coupling which mate with internal threads on the adapter nut.
The internal diameter of the plastic pipe fits over the exterior of the rigid stiffener tube and the O-ring seals form a fluid tight seal with the internal surface of the plastic pipe.
The external threads of the adapter nut will connect with the metal piping systems, such as a metal pipe, a shut-off valve or other component.